Question

Find an explicit function rule for the sequence -3, 3, 9, 15,.... Use the formula a(n) = a(1) + (n-1)d and simplify fully.

Answer 1

a(1) = - 3 ;
a(2) = a(1) + ( 2 - 1 )d ;
3 = -3 + d ;
d = 6 ;
a(3) = a(1) + ( 3 - 1)d;
9 = - 3 + 2d ;
12 = 2d ;
d = 6 ;
a(4) = a(1) + ( 4 - 1 )d ;
15 = -3 + 3d ;
18 = 3d ;
d = 6 ;
Then, a(n) = - 3 + ( n- 1 )6 ;
a(n) = - 3 + 6n - 6 ;
a(n) = 6n - 9 is an explicit functin rule for the sequence -3, 3, 9, 15, ...